An external entity in a Data Flow Diagram (DFD) represents an external system or person that interacts with the system being diagrammed, either by sending data to it or receiving data from it.
Understanding External Entities
External entities are crucial components of DFDs because they define the boundaries of the system and highlight the sources and destinations of the data flowing in and out. According to the reference, these entities are also known as terminators, sources, sinks, or actors.
- Definition: External entities are outside systems that send or receive data to and from the diagrammed system. (Reference: External Entity)
- Purpose: They define the scope of the system being modeled.
- Location: They are typically positioned at the edges of the DFD.
Key Characteristics of External Entities
- Data Source: External entities can be the originators of data that enters the system.
- Data Destination: They can also be the recipients of data produced by the system.
- External to the System: They exist outside the boundary of the system being modeled, meaning their internal workings are not part of the DFD.
Examples of External Entities
- Customer: A customer can provide order information (input) and receive invoices or products (output).
- Supplier: A supplier can send product catalogs (input) and receive purchase orders (output).
- Bank: A bank can receive payment requests (input) and send payment confirmations (output).
- Government Agency: A government agency can receive reports (output) and send regulations (input).
Why are External Entities Important?
Identifying external entities is essential for:
- Defining System Scope: Clearly marking the boundaries of the system.
- Understanding Data Flow: Illustrating the origins and destinations of data.
- Requirements Gathering: Helping to identify necessary inputs and outputs for the system to function.
- Communication: Providing a clear visual representation of the system's interactions with the outside world.
